Update JSONKeyMapper.m
Update JSONKeyMapper.m

simplifying code for reverting map。
johnmyqin/JSONModel,huiping192/JSONModel,jianwoo/JSONModel,liuyujing/JSONModel,dalu93/JSONModel,xunan623/JSONModel,SongYuJie1989/JSONModel,LiuShulong/JSONModel,kerrmarin/jsonmodel,NiuMengFei/JSONModel,xxclouddd/JSONModel,liwangbest/JSONModel,izrie/JSONModel,MellongLau/JSONModel,billinghamj/JSONModel,chenkaige/JSONModel,scottdinggo/JSONModel,ThirakornP/JSONModel,hfossli/JSONModel,ernestopino/JSONModel,billinghamj/JSONModel,jsonmodel/jsonmodel,ramoslin02/JSONModel,db42/JSONModel,youprofit/JSONModel,CareEvolution/JSONModel,AlJaMa/JSONModel,dbachrach/JSONModel,zwcshy/JSONModel,yunzhongyoulong/JSONModel,iwakevin/JSONModel,zwcshy/JSONModel,yarec/JSONModel,MaWenxing/JSONModel,cczallen/JSONModel,icanzilb/JSONModel,jianwoo/JSONModel,SampleLiao/JSONModel,redlinesolutions/JSONModel,SanjoDeundiak/JSONModel,SatanWoo/JSONModel,SummerHF/JSONModel,zhou18520786640/JSONModel,TerryAsh/JSONModel